In, for example, conventional wireless communication handset battery charging, an input is shared with Microphone (Mic) on Vbus pin of Micro Universal Serial Bus (μUSB) connector to save the number of pins and the board area. The Mic and microphone are generic terms used to describe transducers that convert acoustic energy into electrical energy, or more precisely sound waves into electrical signals. Microphones providing high-quality reproduction of sound are desirable in wireless communication applications such as cell phones.
Battery charging circuitry intelligently controls the charging function to deliver optimal battery charging while also protecting the system from an excessively high voltage supply input. The battery charging input can be either a supply from an AC/DC or DC/DC adapter or a Vbus from micro USB connector.
A conventional battery charger circuit example is shown in FIG. 1. As illustrated the battery charger circuit requires a capacitor of the magnitude 1 μF on the Vbus pin. The capacitor is suitable for two reasons: the first reason may be to take Electro Static Discharge (ESD) between the Vbus pin and a ground pin; the second reason is to work as a supply filter on the Vbus pin.
The microphone produces electrical signals for example in a frequency ranging from 100 Hz to 8 KHz. To multiplex the microphone with the Vbus, it is desired to isolate or open the capacitor when the microphone is connected. Typically external off chip solutions are used to isolate the 1 μF capacitor when the microphone is connected. One such example is illustrated in FIG. 2. As illustrated, a power switch SO is used in series to isolate the capacitor when microphone is connected on the Vbus. Although this solution is simple, it requires an extra power transistor and extra control, including signalling and logic, to open or connect the charging path and the capacitor. It also results in an increased board area. To omit disconnecting the capacitor may alter the impedance when operating in microphone state which may decrease the signal/sound quality and/or level.
Another implementation is illustrated in FIG. 3. As illustrated a switch SO is provided in series with the capacitor. The switch may not necessary be a power transistor, however it should have low Effective Series Resistance (ESR). Again this design is simple, however it requires an extra transistor with low ESR and extra control, including its signalling and logics, to open or connect the capacitor that results at least in an increased board area.
It is therefore a desire to provide a circuitry which enables a shared connection pin for different purposes with less complexity in sense of any of signalling, logics, and components for adapting to the different purposes.